In the decades long quest for increasing engine efficiency while at the same time meeting ever more stringent emissions standards, engines have been controlled electronically through the use of electronically controlled injectors to carefully meter and time the introduction of fuel for optimum efficiency and a reduction of exhaust components considered harmful for the environment. Such fuel systems may be a unit injector wherein the injection pressure is developed at the cylinder or in various common rail systems in which the pressure is generated elsewhere.
In both instances, particularly for diesel engines, the fuel timing and quantity is especially important given the varied environmental and operational environment for the engine. The need for precise and flexible control is even more important in the case of diesel engines having exhaust gas recirculation (EGR). Such systems are important to reduce the oxides of nitrogen by reducing the combustion temperatures for the engine. While the oxides of nitrogen are properly reduced there is an increase in the quantity of particulates in the engine exhaust. Such increase requires various aftertreatment devices including particulate filters and in some cases catalysts. The problem with the use of devices of this type is that variations in the composition and flow of the exhaust, including the presence of un-burnt hydrocarbons, can be influenced by individual cylinder misfire. This is when the proper combustion does not occur for a variety of reasons, all of which can cause a variation in the composition of the exhaust flow and therefore the need for adjustment of the engine management strategy to remediate exhaust flow composition.
It is difficult to detect cylinder misfire with the standard fuel system components for controlling the operation of the engine. As a result, additional components, usually in the form of pressure and/or temperature sensors in the exhaust flow are employed to determine the existence of a misfire by fluctuations in pressure and/or temperature. Such systems add additional complexity and cost to the system in addition to providing a further failure mode in that the additional sensors are exposed to the most harmful portion of the exhaust flow.
What is needed therefore, in the art, is a system and method for simplifying and making effective the determination of cylinder misfire.